Beam Load Calculator
How much load can a wood beam carry? Max distributed and point loads for C16-D40 timber, bending + deflection checked. Free.
Enter the span, the beam's width and height and the timber grade, and get the maximum allowable load as a planning estimate. The calculator checks bending (design strength fmd = kmod x fmk / yM with kmod = 0.8 and yM = 1.3, EN 338 grades) and deflection (limit L/300) and reports whichever governs - in kg/m and kN/m, or kg and kN for a center point load. The self-weight of the beam itself is subtracted automatically.
FAQ
How much weight can a wooden beam carry?
It depends on span, section and grade. A C24 50 x 200 mm joist over a 4 m span carries roughly 1.4 kN/m (about 140 kg/m) before the L/300 deflection limit is reached, while the same section over 2 m carries several times more, because capacity falls with the square of the span. Shorten the span or deepen the beam and the allowable load rises fast.
What does grade C24 mean?
C24 is a European strength class (EN 338) for softwood with a characteristic bending strength of 24 N/mm2. The number after the letter is the strength, so C30 and C40 are stronger. D-grades (D24-D40) are hardwoods - denser and heavier for the same strength number.
What size beam do I need for a 4 meter span?
For a typical residential floor load around 2 kN/m including self-weight, a C24 joist of 75 x 235 mm or two 50 x 200 mm side by side are common starting points. Use the calculator to test your exact section: increase the height before the width, because the section modulus grows with the square of the height.
Why is a beam stronger on edge than flat?
Section modulus is W = b x h2/6. Laying a 50 x 200 beam flat swaps the two dimensions, so W drops from about 333,000 mm3 to 20,800 mm3 - a 16-fold loss. That is why joists and rafters always stand on edge.
Is this a structural calculation?
No - it is a planning estimate. The tool applies Eurocode-style factors (kmod = 0.8, yM = 1.3) and an L/300 deflection limit, but ignores shear, bearing, lateral buckling, notches, holes and load duration. Anything you build to must be verified by a structural engineer against your local building code.